Modest but increased prevalence of PD among patients with RA compared to the general population, unrelated to secondary Sjögren’s syndrome. Indeed, the prevalence of the SE HLA-DRB1-04 is increased in both RA and PD, and exacerbated T-cell responsiveness with high tissue levels of IL-17 and exaggerated B-cell/plasma cells responses are found in both the synovium and gingival tissue affected with PD. This evidence concerns the gene HLA-DRB1 and rheumatoid arthritis.